Field of the Invention
The present invention relates generally to peristaltic pumps and more particular to a system and method for holding tubing for a peristaltic pump that enables each tubing to stretch and then holding of the tubes due to peristaltic tube elongation. The present invention compensates for tube stretching and improves dispensing accuracy.
Description of the Prior Art
Fluid dispensing in the pharmaceutical and other markets such as biotechnology are moving away from positive piston pumps and moving to peristaltic pump systems. The main driving force is that peristaltic pump systems do not create shear in the fluid being pumped, and the cleaning validation is simplified as compared to positive piston displacement systems. In seal-less positive displacement pumps, it has been demonstrated that the dispensing fluid experiences shear forces that have an adverse effect on delicate cell structures. Peristaltic pumps, on the other hand, use a series of rollers to compress tubing that passes through the pump to move a fluid. There are many companies that make peristaltic pumps such as Watson Marlow and Cole Parmer which use the same principle of compressing tubing to advance fluid. It has been demonstrated in numerous studies that the use of a peristaltic pump allows for the effective handling of protein and cell structures without the shear forces of piston pumps. Peristaltic pumps have a fluid path only consisting of the tubing that can easily be sterilized, and in many cases discarded after use. This makes the cleaning validation much simpler and reliable.
As peristaltic pumps are being used more for various products, there is a need to carefully support and control the tubing that is being used in the pump. Peristaltic pump tubing needs to be held at the input to the peristaltic pump so that when the tubing is compressed it does not advance into the pump. Some manufacturers such as Watson-Marlow, Cole-Parmer and others use tubing clamps or a Y structure that the tubing must be carefully inserted into and around two fixed posts, one post being at the input and the other at the output. When a tube is used in many peristaltic pumps, the closure mechanism is a pressure shoe that presses onto the tubing; the mechanism stretches the tubing. All tube holding mechanisms can have a negative effect of restricting the flow due to holding the tube too tight.
There are a number of attachment devices known in the art designed to secure and hold tubing, but none of the systems provides for tubing elongation when the peristaltic pump is exercised, and then holding the tube. Action of the pump can force the tubing to elongate in the direction of rotation. This can be seen in the field where the Y is stretched tightly around the two fixed posts before running; but after running, the tubing is loose at the output post showing it was stretched. If individual tube holders are used, the output clamp will exhibit a loose-tube condition present as the tube stretches during use. In some units such as the Colanar peristaltic pump FSP-1001, the rollers are geared so that the forward stretching is less than in non-geared systems, nevertheless elongation still takes place. Tubing stretch occurs in all peristaltic pump systems, and none of the systems currently known in the art have a way of compensating for this stretch. Many of the systems offer a drip retention or suck-back feature where the rollers in the pump are reversed at the end of a pump run in order to move the fluid back into the output tubing. In these cases, drip retention is part of the relaxing of the tube elongation and movement of fluid back into the tube. Tube stretching and relaxing leads to a loss of accuracy since it has the effect of causing variability in each fill.
The Watson Marlow Flexicon system, shown in figure four, has a method of holding the tubing in a peristaltic pump where the input side is held fixed, but there is no output restriction introduced into the fluid passage.
The Watson Marlow 505 type peristaltic pump uses a “Double-Y” set of peristaltic tubing that is secured in the pump by stretching the tubing set over a set of retention pegs. The distance is predetermined and if single tubes are used in the Watson Marlow 505, the nominal distance between tubing clamps is 145 mm for bore sizes up to 8.0 and 150 mm for 9.6 mm bore tubes. In most cases each peristaltic tube is held firmly at the input to the peristaltic pump and slightly stretched and secured with output clamps. Shown in FIG. 1 are Double-Y tubing sets from Watson Marlow that are inserted into the peristaltic pump. The pressure shoe is not shown.
When using Marprene tubing with the 505Di pump, the tubing must be readjusted: “after the first 30 minutes of running, re-tension the tube in the pump head by releasing the tube clamp on the delivery side a little and pulling the tube tight . This is to counteract the normal stretching that occurs with Marprene which can go unnoticed and result in poor tube life and accuracy degradation.”
All manufacturers use some form of mechanical clamp to secure the input and output tube at fixed positions. In FIG. 2 is the Watson Marlow 314D pump head with adjustable clamps on both sides of the pump for the input and output tubes.
The Cole-Parmer Miniflex series of pumps also uses mechanical locks for their tube sets, but in each case lower tube holders are spring loaded vertically in place so they do not compensate for tube elongation. Refer to FIG. 3.
Gibson and Bannistar use a method of tube races to secure the tubing and assure that it stays aligned. U.S. Pat. No. 7,513,757 describes a different method of tube holding.
It would be advantageous to have a system and method where the tubing can elongate. The mechanism would minimally restrict the elongation, but will compensate, and in some cases, measure the elongation. The tubing is also held so that movements backwards or during a “drip retention” operation cannot take place due to one-direction bearings known at clutch bearings. If the tubing is small in nature, or does not provide the necessary tube stretching forces to advance through the tube holders, other forces such as a negator spring can be used to complete the tube holding.